Recently, a boosting circuit is generally required in an application circuit such as a liquid crystal display and the like, to drive LEDs (Light Emitting Diodes) for backlights of a liquid crystal display panel, and the brightness of the LED may be adjusted usually according to displaying requirements of the display panel in different cases.
Particularly, as illustrated in FIG. 1, which is an schematic diagram of a basic structure of a boosting circuit as known, the boosting circuit comprises a boosting chip U1, a energy-storage inductor L1, a freewheeling diode D1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first resistor R1, a second resistor R2 and a third resistor R3, and the like, wherein:
one terminal of the energy-storage inductor L1 is connected with the signal inputting terminal (Vin) of the boosting circuit, the other terminal thereof is connected with the pin (Vsw) of large current switch of the boosting chip and is further connected with the signal outputting terminal (Vout) of the boosting circuit through the freewheeling diode D1. The first capacitor C1, the first resistor R1 and the second resistor R2 are all located on the same side to the signal outputting terminal; one terminal of the first capacitor C1 is connected with the cathode of the freewheeling diode D1, and the other terminal is grounded; one terminal of the first resistor R1 is connected with the cathode of the freewheeling diode D1, and the other terminal is grounded through the second resistor R2, and the ungrounded terminal of the second resistor R2 is connected with the signal feedback pin (VFB) of the boosting chip U1. Further, the power supply inputting pin (VCC) of the boosting chip U1 is connected with the signal inputting terminal, the loop compensating pin (VC) is grounded through the second capacitor C2 and the third resistor R3 which are connected in series, and the signal inputting terminal is grounded through the third capacitor C3.
Particularly, in the boosting circuit shown in FIG. 1, the object of boosting can be achieved by controlling on and off of the internal integrated field effect transistor M1 (not shown in FIG. 1) in the boosting chip U1. Specifically, when the internal integrated field effect transistor M1 in the boosting chip U1 is turned on, the freewheeling diode D1 is reverse cutoff, the current of the energy-storage inductor L1 increases continually, and the energy-storage inductor L1 stores energy. When the internal integrated field effect transistor M1 in the boosting chip U1 is turned off, the energy-storage inductor L1 charges the first capacitor C1 on the signal outputting terminal side through the freewheeling diode D1 to complete the energy transfer. By switching on or off the internal integrated field effect transistor M1 in the boosting chip U1 repeatedly and feedback controlling, an effect that the output voltage is steadied at the set case (at this time, the boosting circuit is in the stable operation state) can be realized. In details, when the boosting circuit is in the stable operation state, the feedback voltage received externally by the signal feedback pin (VFB) of the boosting chip U1 would finally be steadied around the internal feedback reference voltage (a set value associated with the boosting chip) of the signal feedback pin (VFB) of the boosting chip U1. Commonly, the feedback voltage at this time may be considered as being identical to the internal feedback reference voltage of the signal feedback pin (VFB) of the boosting chip U1.
The applicants find that, in the known boosting circuit, for example, as illustrated in FIG. 1, the input voltage is boosted typically in a manner of a wide input voltage range and a fixed output voltage. That is to say, the output voltage of such boosting circuit generally cannot track changes of input voltage when the input voltage changes. In particular, when the output voltage of the boosting circuit is required to be adjusted, it is usual that parameters of each electronic component in the boosting circuit should be reconfigured, such that the application scope of such boosting circuit is not broad, which decreases user's experience.